Recently, in the field of audio equipment, digital audio disc playback systems utilizing pulse code modulation (referred as PCM hereinafter) technology to playback sound as faithfully as possible have been developed. Of these systems, playback systems employing digital audio discs, so-called as compact discs (compact disc will be referred as CD hereinafter), have become especially popular.
Specifically, the CD used in the digital audio disc playback system is typically formed in the type of record disc which is made from a transparent resin and has a diameter of 12 cm and a thickness of 1.2 mm. The CD has a thin metal film deposited on at least one surface thereof, and pits or recesses are formed in the thin metal film, corresponding to digitized data (PCM data) so that logic 1 and 0 may produce different light reflectivities. The PCM data are read out from the CD, when the CD is rotated at a variable rotation frequency of 200 to 500 rpm with a constant linear velocity. The PCM data of the CD are read by an optical pickup incorporating a semiconductor laser or photoelectric transducer device which traces the record track of the CD and moves rectilinearly from the inner side toward the outer side of the CD during the tracing.
The CD stores a large quantity of information that it permits a stereophonic playback for about one hour even if only one side of the CD is used for information storage.
It has been theoretically proved that the CD is much superior to the conventional analog phonograph record in both playback characteristics and information storage density.
In view of the excellent characteristics of the CD, it has been suggested to use CDs in an automatic multi-CD playback system for personal and/or business use. It is possible to realize the automatic multi-CD playback system by means of an autochanger type CD player. An autochanger mechanism in the CD player automatically selects a desired CD in a cartridge accomodated in the CD player and carries the selected CD to the playback position. When the playback of the selected CD is finished, the autochanger type CD player returns the CD from the playback position to the original position in the cartridge if the autochanger mechanism is installed to the main unit of the CD player in advance with plural number of CDs contained.
Conventional autochanger type CD players of this kind are complex in structure and bulky, however, partially because they have been designed for use with analog phonograph records.
Therefore, the conventional autochanger type CD players present control problems. Further, the requirement of more certain operation limits the number of CDs held within such a CD player. Another problem is the long time it takes to exchange one CD for another.
For these reasons, if the conventional autochanger type CD player is applied to CDs without changing the essential structure of the CD player, there arise numerous problems. Hence, the development of an autochanger type CD player suitable for CDs is a matter of urgency.
In these autochanger type CD players, the autochanger mechanism carries out some complicated processes as follows. First, the autochanger mechanism pulls out a desired CD from a cartridge which houses a number of CDs therein. The CDs are stored in the cartridge by being raised on exclusive carrying trays, respectively. That is, the autochanger mechanism pulls out a tray supporting a desired CD. Then, the autochanger mechanism carries the CD together with the corresponding tray to a playback position. For example, the autochanger mechanism lowers the CD on a turntable of a playback section. When the playback of the CD has finished, the autochanger mechanism lifts up the CD from the turntable to a prescribed height position. And then, the autochanger mechanism returns the CD into the storing position in the cartridge where the CD was originally housed.
As described above, complicated motions are needed for the automatic CD change. In connection with this, the autochanger mechanism requires a large number of parts. Furthermore, there will be such a problem that the size thereof may become large in scale so that the size of the entire CD player is enlarged.
The same circumstances apply to video CD players and optical CD document file systems which are soon to be put into practical use.